Cardiac pacemakers and other such implantable medical devices (e.g., cochlear implants, neurostimulators, active drug pumps, etc.) typically comprise a hermetically sealed container and a feedthrough assembly having one or more feedthrough terminals (e.g., niobium pins) that provide conductive paths from the interior of the container (e.g., from an anode lead embedded in an internal anode) to one or more lead wires exterior to the device. In the case of a cardiac pacemaker, these lead wires conduct pacing pulses to cardiac tissue and/or sense cardiac rhythms. To reduce the effects of stray electromagnetic interference (EMI) signals that may be collected by lead wires coupled to the feedthrough terminal pins, it is known to equip a feedthrough assembly with an EMI filter comprising a capacitor that permits passage of relatively low frequency electrical signals along the terminal pins while shunting undesired high frequency interference signals to the container.
Two types of capacitors are generally used: chip capacitors and discrete or monolithic discoidal capacitors. Chip capacitors typically comprise a rectangular ceramic monolithic that is fixedly coupled (e.g., glued) to the ferrule to electrically couple the ferrule to a terminal pin. Such capacitors are fairly inexpensive and occupy a relatively small volume in an implantable medical device. However, chip capacitors are effective for filtering EMI signals over a relatively narrow band of frequencies and, consequently, are fairly limited in application.
Discoidal capacitors have been developed as an alternative to chip capacitors. In the case of a feedthrough assembly comprising a single terminal pin (i.e., a unipolar feedthrough assembly), a discrete discoidal capacitor may be utilized that includes a terminal pin aperture therethrough configured to receive the terminal pin. In the case of a feedthrough assembly comprising multiple terminal pins (i.e., a multipolar feedthrough assembly), a monolithic discoidal capacitor is utilized that includes a plurality of terminal pin apertures therethrough each configured to receive a different terminal pin. In contrast to chip capacitors, discoidal capacitors are effective for filtering EMI signals over a relatively broad range of frequencies; however, monolithic discoidal capacitors are relatively large and expensive to produce.
It may be desirable to leave one or more terminal pins within a multipolar feedthrough assembly unfiltered, such as, for example, those which act as RF antennas to permit communication with the implantable medical device. Additionally, it may also be desirable to equip the various feedthrough terminal pins of a multipolar feedthrough assembly with varying degrees of EMI protection depending upon, for example, the electrical tolerance of the circuitry associated with a particular pin and/or the susceptibility of each pin to EMI interference. In an implantable pacemaker/defibrillator comprising six terminal pins, for example, four pins may be utilized for low-voltage (e.g., around 12 volts) sensing/pacing, while the remaining two pins may be utilized for high-voltage (e.g., around 850 volts) defibrillation. Thus, the four sensing/pacing pins each require only a low-voltage capacitor, while the two defibrillation pins require each a larger, high-voltage capacitor. Traditionally, such a feedthrough assembly has been outfitted with a unitary, high-voltage monolithic capacitor as described above that provides EMI filtering for each of the six terminal pins, including the four low-voltage terminal pins. This may result in an increase in volume and cost that is functionally unnecessary.
Considering the above, it should be appreciated that it would be desirable to provide a multipolar feedthrough assembly having a customizable EMI filter and a method for manufacturing such a feedthrough assembly. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.